The present invention relates to a method of detection of a limited slip differential device, a method and an apparatus for detecting decrease in tire air-pressure employing the method of detection and to a program for judging decompression of a tire. More particularly, it relates to a method of detection of a limited slip differential device, a method and an apparatus for detecting decrease in tire air-pressure employing the method of detection and to a program for judging decompression of a tire with which it is possible to detect whether a limited slip differential (LSD) device is mounted or not and to accurately judge decrease in internal pressure of a tire of the vehicle.
It is conventionally known that a decrease in air-pressure of a tire results in a reduction in the dynamic load radius of the tire so that the rotational velocity or the rotational angular velocity becomes faster when compared to a tire of normal air-pressure. Various methods for detecting decrease in internal pressure on the basis of relative differences in rotational angular velocities of the tires have been proposed (reference should be made to Japanese Unexamined Patent Publication No. 100620/1998, Japanese Unexamined Patent Publication No. 66714/1997, Japanese Unexamined Patent Publication No. 164720/1996 and Japanese Unexamined Patent Publication No. 145654/1996 and others). From among those techniques, the apparatus for detecting decrease in tire air-pressure (DWS) as recited in Japanese Unexamined Patent Publication No. 100620/1998 is so arranged that upon judging that a decompressed wheel when the vehicle is running on a corner is a following wheel, a turning radius is obtained from the rotational angular velocity of the driving wheels, a lateral directional acceleration when running on a corner (hereinafter referred to as “lateral G”) is calculated on the basis of the turning radius, and the judged value is calculated on the basis of the lateral G including no errors by employing a specified threshold.
However, some of the current vehicles are mounted with a limited slip differential device at a differential gear of a driving shaft for the purpose of improving running performances on cornering or the like. A limited slip differential device is functionally so arranged that differential is limited until a differential torque exceeds a set value and the driving wheels rotate at identical speeds on the right and left. In a vehicle mounted with such a device, the rotational angular velocity on the outer side of the turning will be slower than the original rotational angular velocity due to influences of the limited slip differential device so that the turning radius is calculated to be larger than it actually is. Since errors are accordingly generated in judged values, it will be impossible to accurately judge decrease in internal pressure. Moreover, since actions of the right and left wheels will be restricted by the function of the LSD when one of the driving wheels has decompressed, a rotational difference between right and left wheels which shall be caused through the difference in air pressure will be smaller than it should normally be. The threshold of decompression of the driving wheels of a vehicle mounted with such a LSD should accordingly be set to be smaller than a threshold for vehicle which is not mounted with a LSD.
In this manner, a LSD largely affects performances of the DWS. Thus, if the LSD is a standard accessory of a vehicle, design shall be performed on the premise that the LSD is mounted. However, if the LSD is optionally mounted to a vehicle, a microcomputer into which a DWS capable of corresponding to the LSD needs to be mounted to the vehicle upon mounting LSD thereto, while a microcomputer with a DWS which does not correspond to the LSD is mounted to a vehicle which is not mounted with a LSD.
Such a DWS is often mounted to a microcomputer of an ABS. However, it is operationally difficult to distinguish an ABS microcomputer on the basis of use and non-use of a LSD.